Method of protecting metallic surfaces against tarnishing and corrosion



Patented July 5, 1949 METHOD OF PROTECTING METALLIC SUB- FACES AGAINSTTARNISHING AND COR- ROSION Jonas Kamlet, New York, N. Y., assignor toBoyle- Midway Inc., New York, N. Y., a corporation of Delaware NoDrawing. Application August 8, 1945,

- Serial No. 609,717

1 Claim. 1

This invention relates to solid compositions of matter adapted toprevent the tarnishing of metallic surfaces, especially silver surfaces,during storage.

One purpose of this invention is to provide solid compositions which maybe placed in a cabinet, chest or other container together with the metalto be protected and which will by their presence retard or prevent thetarnishing of the surfaces of such metal, especially the surfaces ofsilver.

Another purpose is to provide solid compositions which will retard orprevent by their presence in the neighborhood of the metal to beprotected the discoloration, oxidation, rusting, etching or similarattack on such metal by acidic components of the atmosphere.

A further purpose of this invention is to provide compositions of matterin solid form which will obviate the drawbacks and disadvantages ofliquid and waxy preparations heretofore employed for the prevention oftarnishing of silverware. I

A further purpose of this invention is to pro- -vide a method andmaterial for protecting metals,

especially silverware, against corrosion, which obviates the necesssityof mechanically applying coating material to the metal surfaces as bybrushing, spraying or dipping.

As is well known, silver surfaces are subject to discoloration uponexposure to hydrogen sulfide, sulfur dioxide and other acidic gasespresent in the atmosphere, especially in urban and industrial areas.This discoloration, or tarnishing, is

changes in the nature of metallic surfaces are often initiated oraccelerated by the presence of acid-reacting compounds in theneighboring atmosphere, especially when conditions of high humidityprevail. Metallic or metal-coated objects on storage or in transit arethus often etched so badly that they may no longer be used for thepurpose originally intended.

Although the Accordingly, it is an additional purpose of this inventionto provide solid compositions of matter which ma be contained in molds,boxes, cans or like containers, which may be tabletted, compressed, orotherwise dispensed in a unitary form, which may be stored, ortransported in conjunction with metallic or metal-coated objects, andwhich will, by virtue of their chemical action on the circumambientatmosphere, retard or inhibit the surface tarnishing. or corrosion ofsuch objects.

' Other and additional objects of the present irivention will becomeobvious in the course of the following description.

Numerous products and methods of widely varying nature have beenproposed for preventing the tarnishing and corrosion of silver and othermetallic surfaces. Thus, by way of example, Gangloff and Hieronymus (U.S. Patent 2,117,657 of 1938) wash silverware in a hydrochloric acidsolution of stannous chloride; Stoughton and Davis (U. S. Patent2,144,642 of 1939) coat silver surfaces with a triethanolamine soapemulsion of a hard wax, such as carnauba or candelilla; Sowa (U. S.Patent 2,339,200 of 1944) applies over the surface of a metal anaqueoussolution of a film-forming hydrophilic colloid and evaporates thesolvent to deposit on the surface a thin continuous film of the colloid.Many other products based on widely divergent chemical and physicalprinciples have likewise been described.

Briggmann (U. S. Patent 2,323,369 of 1943) has described an interestingprocess based on the exposure of silverware in' a confined space to thevapor of a dilute aqueous solution of a volatile amine, such asmorpholine, butylamine, ethylene diamine, propylene diamine, etc. Thepresence of the vapors of the volatile organic amine in the surroundingatmosphere exerts an excellent protective action and efiectively retardsor prevents the tarnishing of the metallic surface.

However, this method has the serious draw-' back of requiring the use ofan aqueous solution in an open container. Obviously, it can thereforenot be employed in silver chests, cabinets, drawers, etc., subject tofrequent jarring and motion. The aqueous solutions of the volatileamines are strongly alkaline and, when spilled, may stain or otherwiseharm the'appearance ofwood and other adjacent materials. 'The acrid odorof the split solution may permeate and spoil foodstuffs and otherwisedamage valuable materials stored in the same container.

container is similarly unsuitable for use in con- The open obviously notsuitable for the housewife who wishes to keep free of tarnish a smallchest of silver cutlery, which may be jarred and moved about constantly.Nor is it suitable, for example,

for the protection of delicate precision instruments from corrosion byacidic gases during a prolonged shipment. By the present invention 1provide products which will be suitable for use by the housewife, whichwill not be subject to spillage or deposition of an undesirable residue,which will be transportable without loss of efil- I cacy and which willrequire no further attention or manipulation after being exposed nearthe silverware or other metallic object to be protected. The basis ofthe present invention is the finding that excellent protection againsttarnishing and corrosion of silver and other metallic surfaces can beobtained with the use of a solid composition containing from 0.1% to 20%of an organic amine important. Excessively volatile amines, such asammonia, ethylamine, methylamine, dimethylamine, etc., are unsuitablebecause they evaporate too rapidly and at a rate much greater than thesublimation rate of the remainder of the compositions. They are alsoexcessively ammoniacal in odor and may impregnate or be absorbed byporous materials or other odor-sensitive matter in the vicinity. On theother hand, all of the aromatic amines and most of the aliphatic aminescontaining polar groups (e. g., mono-, diand triethanolamines, mono-,diand tri-propanolamines, 2-amino-2-methylpropandiol-1,3, etc.) are notvolatile enough and do not liberate sufiicient amine into thecircumambient atmosphere to produce the desired efiect.

I have found that the group of organic amines suitable for use in thepresent invention may be characterized by vapor pressures between about7.5 millimeters and about 60 millimeters of mercury at 20 C. Among thecommercially available amines falling within this category and thereforesuitable for use are: morpholine, N-methylmorpholine, ethylene diamine,and propylene diamine. Unlike Briggmann, I find butylamine to beexcessively volatile and therefore unsuitable for use in the presentinvention (U. S. Patent 2,323,369, page 1, column 1, line 37).

The group of subliming compounds to be associated with the amines of mynew compositions must also meet certain specific requirements.Sublimation is the process whereby a solid passes directly into thegaseous or vapor state without liquefying. In the strictest sense, allsolids sublime to some extent, but in most cases the rate i 4 ofsublimation is infinitesimal and imperceptible over prolonged periods oftime.

Such compoimds or mixtures of compounds as will sublime at normaltemperatures and pressures at rates suitable for the present inventionare those having vapor pressures above 0.15 millimeter of mercury atreference temperature of 35 C. However, compounds or mixtures ofcompounds which are excessively volatile are quite unsuitable since theywill sublime too rapidly for effective use in commercial preparations.Thus, I'have found that such compounds are excluded by limiting mysubliming compounds to those having a melting point above about 50 C.

I at atmospheric pressure.

Among the subliming compounds eminently suitable for use in the presentinvention, two general groups may be indicated herewith:

(a) Compounds which sublime quite rapidly, such as paradichlorbenzene(M. Pt. 53 0.; vapor pressure-37.5 mm. at 30.3 C., 52.2 mm. at 35.3 C.,100.0 mm. at 45.3 C. (Speranskl, 'Zeitschrift fur physikalische Chemie,51, 4'! (1905)), and sym-trioxane (M..Pt. 6162 C.; vapor pressure 13 mm;at 25 C., 31 mm. at 3'7.5 C. (Walker and Carlisle, Chemical andEngineering News, 21, 1250, August 10, 1943) (b) Compounds which sublimerather slowly, such as naphthalene (M. Pt. 80.2 C.; vapor pressure-0.21mm. at 35 C., 0.32 mm. at 40 C. (Allen, Journ. Chem. Soc. (London)77.400 (1900)), and camphor (M. Pt. 174-l7'7 0.; vapor pressure 0.38 mm.at 35 C. (Allen, Journ. Chem. Soc. (London) 7'7, 413 (1900)).

By a proper admixture of rapidly-subliming and slowly-sublimingcompounds, the solid composition may be made so as to sublime at anydesired rate. Compounds and mixtures which sublime slowly require moreof the amines than do those that sublime rapidly. Preferably the primary amines, like ethylene diamine and propylene diamine, are used inconcentrations between 0.1% and 10.0%; the secondary and tertiaryamines, like morpholine and N-methylmorpholine are used inconcentrations between 2.0% and 20.0%. These proportions are subjecttoconsiderable variation and extension without departing from the scope ofmy invention, but the solidified mixture should be homogeneous andshould not separate out undissolved amine upon cooling.

In preparing these compositions the organic amine may be dissolved inthe subliming compound or mixture of compounds while the latter is keptin a molten state, the solution being stirred until homogeneous and thenpoured into molds, cans or other containers, where it is cooled.

The compositions may be colored or, perfumed in any desired manner,although the subliming compounds themselves often possess quite pleasantodors (e. g. camphor, trioxane). Additional or ancillary agents may beadded without changing the nature of the present invention.

In choosing a dye for these compositions their alkaline nature must beconsidered. Basic or neutral oil-soluble dyestuffs are most suitable.Thus, 0.01% to 0.02% of dry indigo powder dissolved in the moltencompositions prior to cooling, imparts a pleasant stable indigo bluecoloration thereto.

The compositions, while still in the molten state, may be poured intotheir ultimate containers or they may be poured into molds or frames,cooled, solidified, comminuted and compressed into tablets or pellets ofa unitary size. The cooled solid may also be cut into blocks, shaped orotherwise changed in physical form to suit the marketing requirements ofa product of this'gena h eral nature.

Y The tins, boxes or cans containing these products may be storedindefinitely if kept tightly closed. when ready for use,' the cover ofthe receptacle is removed, or orifices opened therein (e. g. by punchingholes) and the composition 7 commences to sublime. Blocks, tablets orpellets of these compositions may be wrapped in impervious plastic ormetallic films and stored indefinitely in this state. Removing thewrapper activates the block or tablet for use.

Tins or blocks of these compositions may be placed in silver chests. inbureau drawers, in

display cases, in cabinets and receptacles of any nature, stationary ormobile, without fear of spillage. They will evaporatewithout trace andwithout saturating the surrounding atmosphere with water vapor. They maybe wrapped with metallic or metal coated instruments, tools, equipment,etc., to keep them free of corrosion Example ilgrams-oftrioxane areheated on the waterbath until moltenfand 100 grams of morpholine aredissolved therein. The solution is colored by the addition of 0.1% ofdry indigotin powder.

then poured into cans, where it is cooled and permitted to crystallize.The containers are sealed as soon as possible after pouring. An openedupon prolonged storage or transportation and (in a powdered orcomminuted form) they may be scattered into inaccessible crevices andcorners without fear of clogging, corroding, or otherwise injuringmoving parts.

My compositions appear to afford a' three-fold protection to silversurfaces. The presence of 'the volatile organic amine in thecircumambient atmosphere serves to neutralize any acidic gases which maybe present and will continue to do so until the composition hasdissipated completely.

It-also' appears that silver objects adsorb on their surface a thinlayer (perhaps no more than one or two molecules thick) of the volatileorganic amine and possibly form a complex cation (such as silvermorpholinium,

etc.) in which the ionization of the silver atom is repressed below thatof the silver atom in silver sulfide. Thus the silver will no longertend to react with hydrogen sulfide in the atmosphere to form a tarnish(which is usually silver sulfide).

Finally may be mentioned the contribution of the subliming compounds tothe protection of the surface. Metallic and metal-coated objects almostinvariably have a lower specific heat or better thermal conductivitythan the surrounding atmosphere. Thus, in a receptacle or containerwhere convection currents are set up by the sublimation of a volatilecompound, some condensation of the subliming compound will usually occuron the colder metallic surface. This condensation is imperceptible inextent and in no way dims the luster of the polished metal, butsensitive reagents will invariably show the presence of the sublimingcompound on the metallic surface it the composition has been exposedwithin its vicinity.

This surface layer of condensed subliming compound is not static. Itresublimes and is continually replaced by freshly condensing layers.Thus, it provides a third barrier between the metallic surface and thecorosive gases of the surrounding atmosphere."

It is to be understood that the explanations advanced above are notintended to limit my invention, but to offer a. possible explanation ofthe mechanism of the observed protective action.

can of this material is placed in a closed chest containing domesticfiat silver.

Example II 950 grams of para-dichlorbenzene are heated on the waterbathuntil molten, and grams of morpholine are dissolved therein. '8 grams ofcoumarin and 2.0 grams of vanillin are added to the melt, and when aclear solution is obtained it is poured into its ultimate containers.These are sealed and cooled as rapidly as possible to solidify thecomposition.

Example III 475 grams of para-dichlorbenzene, 4'15 grams of trioxane,and 50 grams 'of morpholine are heated together on the waterbath until ahomogeneous solution is obtained. 5 .grams of ethyl vanillin and 0.1gram of fiuore'scein are added and dissolved with stirring. The solutionis then poured into its ultimate containers, capped an allowed tosolidify by cooling.

Example IV 125.0 grams of morpholine and 875.0 grams of camphor inpowder or comminuted form are re-- fiuxed together for a few minutesuntil completely dissolved. The solution is immediately poured into itsultimate containers; these are sealed and permitted to cool.

Example V 950 grams of trioxane are heated on the waterbath untilmolten, and 50 grams of ethylene diamine are dissolved therein. To thissolution are now added 0.25 gram of tetracl'ilorfluorescein Thefollowing examples will illustrate specific embodiments of my invention,but it is not in tended to limit the invention otherwise than as definedin the appended claims.

5.0 grams of vanillin and 5.0 grams of coumarin.

When a homogeneous solution is obtained it is poured into containers,sealed, and permitted to solidify by cooling.

Example VI 475 grams of naphthalene, 4'75 grams of paradichlorbenzene,50 grams of propylene diamine, 10 grams of vanillin and 5 grams ofcoumarin are heated together on the boiling waterbath until a uniformsolution is obtained.' This-is poured into its ultimate containers,covered an allowed to cool, whereupon it solidifies.

Example VII 950 grams of camphor and 50 grams of N- methylmorpholine areheated together on the oiibath until completelydissolved. The solutionis poured into a mold, solidified by rapid chilling,-

and then cut into blocks of convenient size. Several blocks are placedin open trays in a show case containing scientific instruments havingexposed metal parts, such as sextants, goniometers;microscopes, etc. Theremaining blocks are individually wrapped in glassine paper and storedin a tightly covered tin box.

Example VIII 950 grams of camphor, 25 grams of morpholine and 25 gramsof N methylmorpholine are heated together on the oiibath untilcompletely dissolved,

r 1 0.2 gram oi indisotin powder is added, and when a iuniiorm solutionis obtained it is chilled until it crystallizes. The crystallinematerial is com- 'minuted and the eomminuted material is then compressedinto tablets of convenient size and shape.

I claim:

The method of protecting metallic surfaces against tarnishing andcorrosion which comprises confining the metal surfaces together withcir-' SJIIJOB file of this patent:

8 at least 50' C. and a vapor pressureof at least 0.15 millimeter ofmercury at 35 0., whereby the vapors from the corrosion inhibitordifluse through the circumambient atmosphere and con- 5 tact themetallic surfaces to be protected.

JONAS KAMLET.

REFERENCES CITED The jollowing rei'erenlces are of record in the UNITEDSTATES PATENTS Number Name Date 1,851,493 'Calcott et a1. Mar. 29, 193216 1,903,287 Cox Apr. 4, 1933 1,941,014 Lucas Dec. 26, 1933 2,195,689Bash Apr. 2, 1940 2,323,369 Briggmann July 6, 1943

